The synthesis of saturated fatty acids is catalyzed by the fatty acid synthetase multienzyme complex in the cytosol portion of cells. Reducing equivalents required for this reaction are supplied by the malic enzyme and pentose shunt dehydrogenases. Components of the dissociable Escherichia coli fatty acid synthetase including acyl carrier protein have been separated and intermediate steps have been clarified. Malic enzyme has been isolated from pigeon liver in crystalline form and extensively characterized. In addition to the overall oxidative carboxylase and the oxalacetate decarboxylase reactions, this enzyme also possesses weak activities in the reduction of oxalacetate and pyruvate. The ultimate objective of the proposed work is to elucidate the mechanism and regulation of the fatty acid synthesis pathway in animal cells. For this purpose, studies on the structural organization of chicken liver fatty acid synthetase subunits will be performed. Detailed studies on the apparent negative cooperativity and half-site reactivity of malic enzyme will help us to understand the catalytic and regulatory mechanisms of this enzyme and its role in the generation of NADPH for fatty acid synthesis. Results of these studies will materially enhance our knowledge of the cellular machinery responsible for this important metabolic pathway.